This tutorial video shows you how to deal damage to a player that has fallen for a certain amount of time. The more the player falls, the greater the damage. You should already have an idle and a run animation set up. Basic knowledge of how to use Pixel Game Maker MV is required.
1) Set up a condition between fall and idle (probably contact with tile wall.)
2) Copy fall 2 times sand copy idle 1 time.
3) Make a new variable in the second fall / third fall animation.
4) Make a wait time between fall 2 and fall 3.
5) Set up a condition between fall 2 and fall 3 with your new idle animation.
6) In the idle animation, use invincibility to make the player blink.
7) Then subtract the new variable you made from the player's HP variable.
8) Set the new variable to 0 and go back to the normal idle animation.
(Setting up a visible HP bar and a game over is not included in this tutorial.)